/Engine/Plugins/Runtime/MassEntity/Source/MassEntity/Public/MassEntityManager.h
Adds fragments and tags indicated by InOutDescriptor to the Entity. The function also figures out which elements in InOutDescriptor are missing from the current composition of the given entity and then returns the resulting delta via InOutDescriptor.
void AddCompositionToEntity_GetDelta ( [FMassEntityHandle](API\Plugins\MassEntity\FMassEntityHandle) Entity, [FMassArchetypeCompositionDescriptor](API\Plugins\MassEntity\FMassArchetypeCompositionDescrip-) & InOutDescriptor )